Ingredient review
Guanine
INCI: Guanine
Guanine adds a natural shimmer to makeup and nail products, but it is not a skincare active and offers no moisturizing or anti-aging benefits.
In plain English
Guanine is a natural substance that comes from fish scales. In cosmetics, it is used to give products a shiny, pearl-like glow. You will find it in shimmery eyeshadows, highlighters, nail polishes, and lipsticks. It does not treat skin conditions or hydrate the skin; its only job is to add sparkle.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Risk flags are low for most users, though the finished product can still irritate.
- Source
- natural
- Evidence
- moderate
- Irritation
- low
- Clogging risk
- low
Quick decision guide
Useful, but context matters
Guanine is generally a lower-concern ingredient when the full formula suits your skin.
Plain-English read
Treat this as a practical screening step before you compare products that contain this ingredient.
- Step 1Start with the score, then check the irritation and clogging risk before judging Guanine.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.
Score terms in plain English
Irritation risk
lowLess likely to sting, burn, or bother most users, though sensitive skin can still react.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
Guanine is a crystalline compound that naturally occurs in fish scales and skin. It is harvested and purified for use as a pearlescent pigment in cosmetics, often listed as CI 75170 on ingredient labels.
How it works
Guanine particles reflect and scatter light, creating a shimmering or pearlescent effect on the skin or nails. It sits on the surface of the product and does not penetrate the skin, so it works purely as a visual enhancer.
Pros
Natural origin shimmer
Guanine is derived from fish scales, offering a biodegradable and natural alternative to plastic-based glitters.
Long history of safe use
Guanine has been used in cosmetics for decades and is considered safe for topical use with very low irritation potential.
Cons and cautions
Animal-derived ingredient
Guanine comes from fish, making it unsuitable for vegans and those who avoid animal products in their beauty routine.
No skincare benefit
Unlike active ingredients such as hyaluronic acid or niacinamide, guanine does not hydrate, brighten, or protect the skin.
Best for
- Anyone who enjoys shimmery or pearlescent makeup and nail products
- Consumers looking for a natural-origin shimmer alternative to synthetic glitter
Use caution if
- Vegans and those who prefer to avoid animal-derived ingredients
- People with fish allergies (though highly purified guanine is unlikely to trigger a reaction, caution is advised)
Usage tips
Safety summary
Guanine is considered safe for use in cosmetics at typical concentrations. It has a low risk of skin irritation and is not known to clog pores. However, individuals with fish allergies should exercise caution, and those seeking vegan products should choose synthetic alternatives.
Research notes
Guanine has been used safely in cosmetics for decades. The Cosmetic Ingredient Review (CIR) panel has evaluated guanine and found it safe for use in rinse-off and leave-on products. Most available data focus on its optical properties rather than biological effects on skin.
Common label clues
- Typical concentration
- 0.1% to 5%
- Regulatory status
- Approved as a colorant and opacifying agent in cosmetics worldwide, including by the U.S. FDA and the EU CosIng database.
- Common uses
- Nail polish, Lipstick, Eyeshadow, Highlighter, Lotion
- Environmental note
- Guanine is a byproduct of the fishing industry, which can raise sustainability concerns. However, it is biodegradable, unlike many synthetic glitter alternatives.
Good to know
- Guanine is often labeled as 'natural pearl' or 'pearl essence' on cosmetic packaging.
- Synthetic alternatives like synthetic fluorphlogopite provide a similar shimmer without animal sourcing.
Common questions
What is Guanine in beauty products?
Guanine is a natural substance that comes from fish scales. In cosmetics, it is used to give products a shiny, pearl-like glow. You will find it in shimmery eyeshadows, highlighters, nail polishes, and lipsticks. It does not treat skin conditions or hydrate the skin; its only job is to add sparkle.
What does Guanine do in a beauty product?
Guanine particles reflect and scatter light, creating a shimmering or pearlescent effect on the skin or nails. It sits on the surface of the product and does not penetrate the skin, so it works purely as a visual enhancer.
Is Guanine safe for most people?
Guanine is considered safe for use in cosmetics at typical concentrations. It has a low risk of skin irritation and is not known to clog pores. However, individuals with fish allergies should exercise caution, and those seeking vegan products should choose synthetic alternatives.
Who should be careful with Guanine?
Vegans and those who prefer to avoid animal-derived ingredients People with fish allergies (though highly purified guanine is unlikely to trigger a reaction, caution is advised)
Research sources
Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.